C++按值调用

#include <iostream>

using namespace std;

void swap(int x, int y) {
   int temp;

   temp = x; /* save the value of x */
   x = y;    /* put y into x */
   y = temp; /* put x into y */

   return;
}

// function declaration
void swap(int x, int y);
int main () {
   // local variable declaration:
   int a = 100;
   int b = 200;

   cout << Before swap, value of a : << a << endl;
   cout << Before swap, value of b : << b << endl;

   // calling a function to swap the values.
   swap(a, b);

   cout << After swap, value of a : << a << endl;
   cout << After swap, value of b : << b << endl;

   return 0;
}